Filters are often used to remove solid particles such as e.g. dust, pollen, mold, or sand from an air flow. Especially in applications where air quality is important, notably in building ventilation systems and in engines, filters are often indispensible for the provision of clean air. For example, gas turbines are generally operated with filters for removing particles from an air or gas flow, such that particles are hindered to enter the turbine. With this, potential damage risks such as e.g. turbine fouling, corrosion, and adhesion of the particles to the rotor blades in the gas turbine air compressing device may be impeded. Thus, the filters are provided to maintain the functionality of an electricity generation output from the gas turbine. The filters used are often of a pocket filter type, having a series of filter pockets attached to a frame structure. The filter pockets may be made of e.g. glass fiber, polypropylene, polyester, spunbonded fabric or the like.
After a certain time of operation, dependent on the ambient conditions in which the gas turbine operates, a large quantity of accumulated particles in the filters deteriorate the function of the intake device. In other words, the air or gas flow resistance increases which may, as a consequence, result in an electricity output loss of the gas turbine. Moreover, other ambient conditions such as sand storms, snow storms, rain, heat, cold, or the like may negatively affect the performance of the filters.
In the above-mentioned, or other, situations, the filters may have to be replaced to regain the sought air filter efficiency. However, a filter replacement may raise several problems. If the filter is removed from an intake device during gas turbine operation, the prevention of particles entering the gas turbine at the air intake is impaired. Such a particle intrusion into the gas turbine may lead to a deteriorated gas turbine operation, costly maintenance, and/or possibly, a gas turbine breakdown. On the other hand, the gas turbine may be switched off such that a filter replacement may be made when the gas turbine is not operating, thereby avoiding some problems related to the deteriorating effects of a gas turbine operation without any filter. However, this approach leads to other problems, as ruptures in gas turbine operation usually are cumbersome and problematic. Furthermore, a gas turbine switch-off, leading to an operation standstill, is associated with an economic loss.
In WO 2011/000437, a pocket filter assembly for particle removal is disclosed. The assembly comprises a filter unit and a pre-filter unit, each having a plurality of filter pockets, wherein the filter pockets of the pre-filter unit are arranged within the filter pockets of the filter unit. The disclosed arrangement enables a pre-filter removal from and insertion into the filter unit such that the filter unit may be kept in the in the pocket filter assembly during machine operation, while the pre-filter unit is removed from the filter unit. The pocket filter assembly further comprises metal bars arranged along the filter unit sides such that sideway flexing of the filter pockets of the filter unit is hindered. However, as the handling of the pocket filter assembly disclosed may be relatively cumbersome, alternative solutions for a more convenient arrangement for particle removal may be of interest.